In wireless charging systems, the H-bridge converter's switching frequency is set close to the system's natural resonance for achieving optimized zero voltage switching (ZVS). Variations to the system's natural resonance are commonly tracked by following the changes in the resonant current's polarity, i.e., current zero-crossings. The main implementation challenge is accounting for the time delay between the real monitored current and the final resulting switches’ commutations. This becomes critical at high switching frequencies, particularly when the magnetic coupling and loading vary widely. This paper proposes an auto-resonant detection method that continuously ensures optimized ZVS turn-on with the minimal circulating current over the operable range of magnetic coupling and load. The suggested implementation provides two split variable references for the resonant frequency detection, which adaptatively compensate for the propagation delay based on the resonant current slope. The auto-resonant scheme is benchmarked against the commonly employed method with fixed current detection references. The results highlight the auto-resonant strategy's advantages, namely extended operable range, wider ZVS turn-on region, ease start-up, and improved DC-to-DC efficiency. The auto-resonant features and functionality are verified experimentally with a 200 W low-voltage e-bike wireless charger. Finally, the benefits of the presented method are analytically explored for high-power applications by considering the H-bridge semiconductor losses of a state-of-art 50 kW wireless charging system.@en

In inductive power transfer applications that use resonant compensation networks, the commonly employed H-bridge inverter should be kept operating in soft-switching to ensure high power efficiency and low irradiated electromagnetic noise. To achieve so, the zero-crossing detection circuit for the resonant current or voltage must be fast and accurate in any operating condition. This paper researches the concept of an auto-resonant control for the typical H-bridge resonant converter used in wireless charging systems. In the method proposed here, the reference levels for the zero-crossing detection of the inverter's current are automatically adapted depending on the slope of the current itself at the zero-crossing. In this way, it is possible to compensate for the circuit delay even in the presence of parameters' variation and to ensure that the soft-switching is always maintained. The functionality of this control method is proven first mathematically, and then with circuit simulations. The core steps for the implementation are described with the support of functional blocks. Finally, the system start-up strategy is explained, which uses an auxiliary timed oscillator to modulate the inverter with a fixed 50% duty cycle at a higher frequency than the nominal. This guarantees that the start-up is in the inductive region and, thus, the zero-voltage switching turn-on. Once the detection circuits sense the current flow, the oscillator is automatically disabled, and the nominal power transfer starts.

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This paper presents the use of a new experimental setup for power electronics and electrical drive experiments in teaching Electrical and Electronics Engineering bachelor students. The setup is developed in the context of educational innovation and is configured to closely resemble industrial appliances that are used in power electronic converters for DC-DC, DC-AC and AC-DC conversion. The hardware allows students to perform laboratory experiments with voltage levels below 60 volts and under 200 Watts, to comply with DC grid LVDC standards. Applications range from battery charging, solar panel maximum power point tracker, DC-DC conversion to single phase and three phase AC applications such as motor drives, grid-tied connected inverters and wireless power transfer. Moreover, the applications can be tailored to apply in other disciplines, such as Mechanical Engineering and Mechatronics. A set of experimental assignments guides students from theoretical principles, via idealized simulations to measurements. Finally, students perform laboratory experiments in which they are assessed on their verification of the theoretical and simulation results together with measurement outcomes. Since the setup is constructed in the same way as an industrial application, typical measurement results due to parasitic components, are visible to the students. Compared to commercial educational training hardware, the industrial construction is more close to reality and better prepares students to understand the working of power electronics and electrical drives. The combination of the industrial design approach and multidisciplinary flexibility of hardware, laboratory experiments provide students a realistic and enhanced learning experience.

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If electric vehicles have to be truly sustainable, it is essential to charge them from sustainable sources of electricity, such as solar or wind energy. In this paper, the design of solar powered e-bike charging station that provides AC, DC and wireless charging of e-bikes is investigated. The charging station has integrated battery storage that enables for both grid-connected and off-grid operation. The DC charging uses the DC power from the photovoltaic panels directly for charging the e-bike battery without the use of an AC charging adapter. For the wireless charging, the e-bike can be charged through inductive power transfer via the bike kickstand (receiver) and a specially designed tile (transmitter) at the charging station, which provides maximum convenience to the user.

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Industrial wireless charging systems use standardized coils to guarantee interoperability between different manufacturers. In combination with these coils, the compensation network can still be designed and optimized. This paper explains the step-by-step design of the compensation network for a 7.7 kW wireless charging system (power class WPT2), which is composed of standardized coils. The compensation network must satisfy the output power and voltage requirements, the soft-switching of the inverter, and the limit of voltage and current stress on the components. The S-S compensation network is found to be unfeasible for those coils, and an optimized double-sided LCC compensation network is designed. The 3-phase grid connection is selected despite the 1-phase one because it gives the lowest total conduction losses. Finally, two parallel SiC MOSFETs C3M0075120K are chosen as inverter's switch because of their low conduction losses. This solution can achieve a payback time within a year with respect to the cheapest one.@en

In high-power wireless battery charging that uses inductive power transfer, a considerable amount of power losses are located in the transmitter and receiver coils because they carry high resonant currents and typically have a loose coupling between them which increases eddy current losses. Therefore, the nominal operation needs to be chosen such that the coils' losses are minimized. Additionally, the inverter's semiconductors soft-switching improves both the power conversion efficiency and the electromagnetic compatibility of the system, thus it needs to be safeguarded for a wide operating range. However, depending on the chosen quality factor of the coils, it might happen that the minimum coils' losses and soft-switching are not satisfied at the same time. This paper defines a guideline on the parametric selection of the coils' quality factor such that the optimum operation of both the coils and the resonant converter can be achieved simultaneously. This parametric guideline is proposed for resonant converters implementing the four basic compensation networks: series-series, series-parallel, parallel-series, and parallel-parallel. Finally, circuit examples are provided for an 11 kW wireless battery charging system.

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In charging applications, wireless power transfer (WPT) is mostly used in the form of inductive power transfer with magnetic resonant coupling. Therefore, both the transmitter and the receiver coils are combined with capacitors, such that only active power is transferred. To evaluate the operation of the WPT charging system, its equivalent circuit can be analyzed in the frequency domain. However, this is limiting since the H-bridge inverter operation is not intrinsically considered. As an example, the operating points of both zero current switching (ZCS) and zero voltage switching (ZVS) operations might be still analyzed, but it is not possible to assess their performance in terms of efficiency. In this paper, the advantage of ZVS over the ZCS is evaluated in terms of the efficiency and the delivered output power. To enable the full potential of ZVS, this is tuned considering the switch capacitance and the dead time.

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In the next decades, the number of electric vehicles (EVs) for private use is predicted to increase considerably. Charging the EVs through wireless power transfer (WPT), i.e. wireless charging, has the potential to shorten charging duration of EVs batteries through dynamic charging and it would also improve the safety of static charging in case of wet weather conditions. From 2015, standards and regulations have been released such that common constraints can be defined. Therefore, it is essential to be aware of these regulations before designing an EV wireless charging system, such that it can become an actual application. This paper focuses on the available regulations and standards on EVs charging through WPT. These regulations are explained individually and then, they are compared and discussed mainly in terms of the electromagnetic compatibility (EMC) and exposure of humans to the radiated magnetic field limits. To gain a better understanding, a quantitative and qualitative interpretation of these limits is also given.@en

Charging electric vehicles from solar energy provides a sustainable means of transportation. This paper shows the design of solar powered e-bike charging station that provides AC, DC and contactless charging of e-bikes. The DC charger allows direct DC charging of the e-bike from the DC power of the photovoltaic panels (PV) without the need for an external AC charger adapter. In case of the contactless charger, the bike can be charged without the use of any cables providing maximum convenience to the user. Finally, the charging station has an integrated battery that allows for both grid-connected and off-grid operation@en

This paper proposes a way to supply a vacuum cleaner from a DC grid instead from an AC grid. Problems caused by the transition from an AC supply to a DC supply will be discussed, like the high inrush current during turn-on and the arc that occurs when a mechanical switch is used to turn-off. These problems will be solved in a low-cost manner. Therefore, a power MOSFET is used to control the motor of the vacuum cleaner. A simple PWM controller is used to control the MOSFET, thus the motor. This PWM controller limits the inrush current with a current sensing feature which turns the PWM controllers output OFF when the peak-current exceeds the threshold value. Furthermore, the ON/OFF button of the vacuum cleaner is also connected to the PWM controller. Turning off the vacuum cleaner will also turn off the output of the PWM controller. Because of this the motor will gradually slow down, the current is regulated towards zero and this prevents a current arc. A prototype was build inside the housing of the vacuum cleaner to validate the design. The experimental tests prove the functionality of the circuit by testing the control of the motor and current sensing feature. Finally, de result of the tests will be discussed and recommendation for possible improvements or alternative designs will be given.

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